Aquatic organisms inhabiting in water such as bacterias, seaweeds, shellfishes, etc, attach and breed on water contact portions of various harbor facilities such as quays, piers, platform piers, buoys, and submerged structures such as ships and greatly lower the functions of such facilities and submerged structures.
The quantity of cooling water or power generation water for various intake equipment such as plant intake passes, intake pipes and screens, which is used as cooling water in steam power stations, atomic power stations, iron foundries, oil refinery plants, etc. or as power generation water of power stations, ranges from dozens of thousands of cubic meters to hundreds of thousands of cubic meter per hour and is extremely great. Therefore, maintenance management of the intake equipment is of great importance. The essential points of this maintenance management are corrosion control of the facilities and control of attachment of aquatic organisms attaching and breeding on the surfaces of the intake facilities in the same way as in the submerged structures. Attachment and breeding of the aquatic organisms are causes for the occurrence of various troubles in the normal operations of equipments and facilities.
Excellent corrosion prevention engineerings such as the development of corrosion resistant materials, the progress in coatings and cathodic protection have been developed and put into practical applications as corrosion prevention control means of these submerged structures and Intake facilities.
On the other hand, prevention means against attachment of aquatic fouling organisms such as marine creatures have long been employed. In other words, the following means have been proposed:
(1) adding chlorine or hypochlorites; PA1 (2) coating of anti-fouling paints; PA1 (3) covering with anti-fouling metals; PA1 (4) formation of chlorine or hypochlorite ions by brine electrolysis; and PA1 (5) formation of copper ion using a copper anode. PA1 (1) A prevention and control method of aquatic attaching fouling organisms comprising: covering attaching portions of aquatic fouling organisms on the surfaces of submerged structures or intake facilities with a plurality of mutually insulated metallic covers made of iron, magnesium, aluminum or their alloys through an insulating material and a cushion material; using the metallic covers as electrodes, respectively; composing an electric circuit using a pair of the metallic covers facing each other; connecting the electric circuit to a D.C. power supply having a current reversal function; supplying a current between both of the electrodes either continuously or intermittently; and reversing a current polarity so that when one of the metallic covers is an anode, the surface of the metal constituting the metallic cover is dissolved and activated, and attachment of the aquatic fouling organisms is controlled or prevented. PA1 (2) A prevention and control method of aquatic attaching fouling organisms comprising: covering attaching portions of aquatic fouling organisms on the surfaces of a submerged structure with a metallic cover made of iron, aluminum, magnesium or their alloys through an insulating material and a cushion material; connecting the metallic cover to a positive pole of a D.C. power supply and using it as an anode; connecting the submerged structure to a negative pole of the D.C. power supply to use it as a cathode and to form an electric circuit; and supplying a current between the cathode and the anode either continuously or intermittently so as to prevent or control the attachment of the aquatic fouling organisms to the surface of the anode metallic cover by dissolving and activating the surfaces of the metallic cover. PA1 (3) A prevention and control method of aquatic attaching fouling organisms comprising: covering attaching portions of aquatic fouling organisms on the inner surfaces of an intake facility other than its bottom surface with a plurality of mutually insulated metallic covers made of iron, magnesium, aluminum or their alloys through an insulating material and a cushion material; connecting the metallic covers to positive pole of a D.C. power supply and using them as an anode; disposing iron or an iron alloy material on the bottom surface of the intake facility and connecting it to a negative pole of the D.C. supply to use it as a cathode to form an electric circuit; and supplying a current between the cathode and the anode either continuously or intermittently so that the surfaces of the metals constituting the metallic cover are dissolved and activated, and so that attachment of the aquatic fouling organisms to the surfaces of the metallic cover is controlled or prevented.
All of these methods are effective as prevention means against attachment of marine organisms, but they are anti-fouling means or methods comprising principally the formation of the toxic ions such as chlorine, hypochlorite, copper, mercury, tin, and there is the possibility that these toxic ions induce secondary environmental pollution. The formation and use of these toxic ions require great expenses for installations for keeping a suitable concentration or density for a long service life and for the maintenance and management of the installations; but mainly because they use the toxic ions and may result in environmental destruction rather than because of expenses, the use of such installations tends to be inhibited.
Chlorine and hypochlorites can be charged easily, but the concentration management is difficult. If any reducing agents or substances exist in water, the consumption amount of chlorine becomes greater, and the anti-fouling effect cannot be expected in some cases. A great deal of labor and expenses are necessary for maintenance and management of a chlorine generation apparatus and its concentration management, and secondary environmental pollution is not avoidable. Therefore, the use of such compounds is now avoided as much as possible.
Anti-fouling coatings or paints mostly contain metal pigments generating toxic ions, and comprise mainly mercury, mercury compounds, copper, copper alloys and their compounds. Recently, these materials have been replaced gradually by organic stannous compounds (stannates), but the service life as the coating is about 2 years. These paints involve the problem of low durability resulting from impact, wear and tear. Furthermore, the use of such coatings tends to be inhibited from the aspects of environmental pollution and safety in the same way as in the case of chlorine.
Covering with the anti-fouling metals is the method which applies a covering of copper or a copper alloy to the submerged area of the structure and controls attachment of the aquatic fouling organisms by the toxic copper ion slightly eluting from the surface of copper or the copper alloy. However, this method needs to cover the entire surface of the structure and to perfectly insulate the structure (made of iron steel). (If any defect occurs in the covering metals, unusual corrosion occurs in the underlayer structure.) For these reasons, the cost of the covering work is high. It is one of the anti-fouling methods based on the toxic ion, and secondary environmental pollution is not avoidable.
Anti-fouling means of marine organisms on the wall surfaces of submerged structures, particularly the intake facilities of plants using large quantities of brine as cooling water, most widely employ the formation of chlorine and hypochlorites by electrolysis of brine or the formation of the copper ion by the use of a copper anode.
It is known to generate chlorine, particularly the hypochlorites, by direct electrolysis of brine. Various attempts have been made to attain higher economy and higher safety. For example, Japanese Patent Publication No.(Sho.) 51-41030 (41030/1976) describes a sea water electrolysis system for generating hypochlorites. Similarly, Japanese Patent Publication No.(Sho.) 54-40472 (40472/1979) discloses an anti-fouling and anti-corrosion method using a hypochlorite formation apparatus in combination with an iron ion generating system by sea water electrolysis, and Japanese Patent Laid-Open No. (Hei.)2-236290 (236290/1990) discloses an anti-fouling system using an electrode material obtained by applying an insoluble conductive film and a conductive film made of a highly conductive material to the submerged structure through an insulating film in place of a platinized titanium and carbon electrode as the conventional hypochlorite forming anode.
Sea water electrolytic technique using a copper anode for forming toxic ions has long been known. For example, Japanese Patent Publication No. (Sho.) 41-5193 (5193/1966) describes a prevention method of aquatic attaching fouling organisms by D.C. electrolysis by disposing a copper anode and a cathode in the proximity of inner wall surfaces of sea water intake underdrains or open drains so as to elute the copper ion by D.C. electrolysis, and Japanese Patent Publication No.(Sho.) 45-923 (923/1970) describes a method which disposes a pair of copper electrodes on the inner surface of a sea water intake pipe and supplies an A.C. or a current reversible direct current voltage. Similarly, Japanese Patent Publication No. (Sho.) 43-6374 (6374/1968) describes a method which prevents attachment of aquatic fouling organisms by sea water electrolyzed by copper or copper alloy anode in sea water and adds cathodic protection means by using the objective structure as the cathode.
Japanese Patent Laid-Open No.(Sho.) 59-9181 (9181/1984) describes a prevention method of aquatic attaching fouling organisms on the outer surfaces of submerged metal structures such as ships by applying a plurality of anti-fouling metals (principally copper or copper alloys) on time submerged areas.
Anti-fouling means using other metals in place of copper or using these metals in combination with copper has also been proposed. For example, Japanese Patent Publication No.(Sho.) 48-39343 (39343/1973) discloses a method which prevents fouling of hulls of ships by covering the hulls with a zinc layer, uses the zinc layer as the anode while the ships are at rest by the use of an auxiliary electrode, and uses the zinc layer as the cathode during moving. Japanese Patent Publication No.(Sho.) 59-40361 (40361/1984) discloses another method which feeds a D.C. current to an anode made of copper or a copper alloy and at least one kind of metals selected from the group consisting of zinc, aluminum, magnesium and iron, and disposed in the proximity, or at an intermediate part, of an intake port of a cooling pipe system of sea water or brackish water, which allows the copper ions to be adsorbed and concentrated by hydroxide colloid of the anode metal, and thus enhances the anti-fouling effect of the aquatic attaching fouling organisms and at the same time, inhibits the outflow of the copper ion into sea water.
A method of preventing marine bio-fouling by generating a combination of A.C. and D.C. currents in order to elute controlled chlorine and copper ions into sea water is disclosed in Japanese Patent National Publication No.(Sho.) 63-502172 (502172/1988) (WO 087/03261).
Anti-fouling means of the aquatic attaching fouling organisms by forming the chlorine and hypochlorite ions by the electrolysis of sea water or by utilizing the toxic character of the copper ion, etc, by the electrolysis using copper or the copper alloy as the anode are effective means, but they extirpate useful marine organisms in addition to secondary environmental pollution.
According to Japanese Patent National Publication No.(Sho.) 63-502172 (502172/1988) described above, the action potential of the marine organisms at the nerve/muscle interface is disrupted by the use of the A.C., and the possibility of their attachment of the structures is lowered. This method is said to be the means which controls attachment of the marine fouling organisms but does not extirpates them. As a method not involving the formation of the toxic ions, Japanese Patent Publication No.(Hei.) 1-46595 (46595/1989) discloses a method which, when the metal structures are constructed by valve metals such as titanium, deposit of a precious metal oxide catalyst on the surface of the valve metal, connects the metal structure to the anode of a D.C. power supply, inhibits the formation of chlorine, generates oxygen and hydrogen gases and prevents deposit of marine fouling organisms and scales consisting of calcium compounds. This method is directed to heat exchanger pipes made of the precious valve metal such as titanium. However, it is not industrially preferable to cover the surface of facilities, which are great both in the quantity and in the number, or the surface of the structures which are exposed to marine tidal currents changing incessantly, by the oxide catalyst coating valve metal.
As described above, various anti-fouling means for preventing attachment of the aquatic attaching fouling organisms inhabiting and growing on the submerged areas of the marine structures have been developed, but none of them are entirely satisfactory. In other words, they involve the problems that the toxic ions are generated, secondary environmental pollution may be induced, maintenance management of the equipments is not easy, the running cost is high, and even useful aquatic organisms are extirpated.
For example, intake facilities of power stations, ere, introducing large quantities of sea water as cooling water have the problem of getting rid of aquatic fouling organisms expanding over one thousand meters. At present, the removing operation is mechanically carried out by a manual operation (workers or divers) or using robots. In addition to its low removal efficiency, this method involves a large number of safety problems, requires an enormous removal cost, and needs a disposal and waste site of the marine organisms thus removed. Therefore, not only economical but also industrial losses are very large.